1. Field of the Invention
The present invention relates to an image data processor capable of outputting binary image data of high resolution to a display device, a video printer or the like of low resolution, with suppression of visual recognition deterioration. The image data processor is widely applicable to displaying of data of document files in personal computers, workstations, etc. or facsimile data using liquid crystal displays.
2. Description of the Prior Art
Lately, binary image data input through an image input device such as an image scanner or the like has been processed in many kinds of ways. For example, the binary image data has been directly displayed and edited on a display device, or stored and managed in an external storage, e.g., magnetic disks or optical disks before being output to a display device or a printer as needed. This situation has created a demand for an image data processor such as an image filing system or the like, and an example is disclosed in Japanese Patent Laid-Open Tokkohei No. 3-3256 (3256/1991).
A conventional example of the image data processor will be depicted hereinbelow with reference to FIG. 10.
FIG. 10 is a block diagram of the conventional image data processor, in which reference numerals represent respectively: 100 a central processing unit for controlling the operation of the whole device (referred to as a CPU hereinafter); 101 a cold cathode display device as an image output device (referred to as a CRT hereinafter); 102 a main memory of the CPU; 103 an image memory for displaying images and provided at the side of the display device separately from the main memory 102; 104 an image scanner; 105 a scanner interface (referred to as a scanner I/F hereinafter); 106 an external storage such as a magnetic disk drive, an optical disk drive, etc.; and 107 an external storage interface (referred to as an external storage I/F). It is to be noted here that although most of the latest personal computers use image output devices which store image data in the main memory 102 without having the image memory 103, the description here is related to an image data processor of the type which stores the image data in the image memory 103 and displays the same using the display device. The binary image data read by the image scanner 104 is transferred to the image memory 103 via the scanner I/F 105 or retained in the external storage 106 to be output to the image memory 103 as needed.
The operation of the conventional data processor in the above-described structure will be explained below.
When the input image read through the image scanner 104 is output to CRT 101, there are two manners of display. That is, in one, the image data is thinned to be displayed on the whole screen at one time for facilitation of confirmation of the total layout (referred to as a thin display mode hereinafter), and in the other manner, the original document image is not thinned (referred to as a direct display mode).
In general, when the input image is to be edited, namely, when the input image is to be partly moved, enlarged, compressed or rotated, the aforementioned thin display mode is practiced so that the total layout can be confirmed. For thinning the data, for instance, the original document image data is sampled every predetermined interval, or the original document image space is divided into many small sections and the small sections with one or more black picture elements are made black pixels. The latter method is called an OR method.
Meanwhile, Japanese Patent Laid-Open Publication Nos. 2-267592 (267592/1990) and 3-259193 (259193/1991) disclose to use a smoothing filter to produce multivalued data so that the characters are still easy to see even after they are compressed.
In the thin display mode to confirm the displaying state of the whole image, the binary image data is processed by a simple thinning treatment. Therefore, if the image data of many pixels obtained from a wide area of a character document or the like by an image scanner is output according to the thin display mode, the data of thin lines is omitted and fine parts of the document are broken. As a result, the visibility of the data is greatly hurt because of the lost character and graphic information. Therefore, the thinning amount of data should be reduced to display a narrower area of the document or the thin display mode is switched to the direct display mode to thereby visually confirm only a small part of the image. In other words, it has conventionally been impossible to output the data of fine parts in a manner to allow direct visual confirmation of the data while monitoring a wide range of the image data.
Although it is possible to produce multivalued data from the binary data to obtain a display which is easy to see by using the intermediate tone as is disclosed in the prior arts Tokkaihei 2-267592 and 3-259193 mentioned earlier, drawbacks yet remain to be solved in that the compression rate of the data cannot be set optionally in the former example, and the latter arrangement is complicated because of the use of the smoothing filter, resulting in a large circuit scale and is low processing speed.